Study On Pattern And Forming Mechanism Of Sedge Plant Communities At Chongming Dongtan

Salt marshes are widely distributed all over the world,which have steep environmental gradients,relatively few plant species,and distinct zonation patterns.Spatial pattern of plant community has long been the focus of ecological research.Scirpus triqueter,Scirpus mariqueter and Car ex scabrifolia are three major native sedge plants in Chongming Dongtan.They play an important role in ecosystem function.However,the sedge plants are being threatened by human reclamation,pollution and biological invasion recently,which result in sharp decline of distribution area.Based on the research of controlled environment experiments,we surveyed spatial autocorrelation of environment factors in southern Chongming Dongtan on small scale rather than on large scale,and analyzed the relationship between sedge plants and environment factors as well.We also studied the distribution pattern and intraspecific and interspecific competition mechanisms of salt marsh pioneer species in Chongming Dongtan.The main results of this study were as follows:(1)The spatial and temporal variation of environmental factors and the degree of habitat heterogeneity were high in southern Chongming Dongtan,Tuanjiesha.In isotropic model,water content and NO3--N showed strong spatial autocorrelation,while electric conductivity showed moderate spatial autocorrelation,bulk density and N4+-N showed weak spatial autocorrelation.In anisotropic model,nugget and sill of different environment factors were the same,but the range of water content,electric conductivity,NH4+-N and NO3--N varied except for bulk density.Water content in May and November were significantly higher than in July(one-way ANOVA,P<0.05);electric conductivity and NO3--N varied significantly among different seasons(P<0.05);bulk density in May was significantly higher than in July and November(one-way ANOVA,P<0.05);NH4+-N in July was significantly higher than in May and November(one-way ANOVA,P<0.05);total inorganic nitrogen in November was significantly higher than in May and July(one-way ANOVA,P<0.05).Scirpus mariqueter thrived in habitats with high soil water content,high bulk density and low electric conductivity.Scirpus triqueter dominated in habitats with high soil water content,low electric conductivity and low bulk density.Carex scabrifolia dominated in habitats with high soil ecectric conductivity,low water content and low NH4+-N concentration.(2)Density of clonal plant populations were constantly changing,and the intensity of intraspecific competition also varied in different life stages.Thus,clonal plants would take different growth and regulation strategies.During the whole growing season,different initial planting density treatments had no significant effects on density growth of Scirpus triqueter,but had significant effects on density growth of Scirpus mariqueter and Carex scabrifolia(Tepeated measurement ANOVA,P<0.01).At harvest,ramet density of Carex scabrifolia in medium and high density treatments were significantly higher than in low density treatments(one-way ANOVA,P<0.05).Canopy height of Carex scabrifolia in medium density treatment was significantly higher than in low and high density treatments(one-way ANOVA,P<0.05).Single ramet biomass of Scirpus triqueter and Scirpus mariqueter had significantly negative correlations with their ramet density(R =0.541,P<0.05;R2=0.520,P<0.05),while the total biomass of Scirpus triqueter and Carex scabrifolia were significantly positively correlated with their ramet density(R2=0.525,P<0.05;R2=0.508,P<0.05).Root:shoot ratio of these species did not differ significantly with increasing ramet density at harvest.Three sedge plants all showed intraspecific competition in medium and high density treatments,and they had more intense intraspecific competition in high density treatment than in medium density treatment(one-way ANOVA,P<0.05).(3)Ramets of sedge plants had significant inhibition effects on growth of seedlings,and were also inhibited by seedlings.During the whole growing season,height of Scirpus mariqueter seedlings was significantly lower in mixture with Scirpus triqueter ramets than in monoculture(repeated measurement ANOVA,P<0.05),but no significant inhibition was observed when in competition with Carex scabrifolia ramets mixture and Scirpus mariqueter ramets mixture.Density of Scirpus mariqueter seedlings was significantly higher in monoculture than in Scirpus mariqueter seedlings-Carex scabrifolia ramets mixture during the whole growing season(repeated measurement ANOVA,P<0.01),but not in Scirpus mariqueter seedlings-Scirpus triqueter ramets mixture.Competition treatments had no significant effects on height of three sedge plant ramets,and time×competition interaction had extremely significant effects on height of Carex scabrifolia ramets(repeated measurement ANOVA,P<0.01).Competition treatment had extremely significant effects on density growth of three sedge plants ramets(repeated measurement ANOVA,P<0.01).At harvest,the aboveground biomass of Scirpus triqueter ramets was significantly reduced due to the competition effects of Scirpus mariqueter seedlings(one-way ANOVA,P<0.05),while the highest height and canopy height of Scirpus mariqueter seedlings was significantly reduced due to the competition effects of Scirpus triqueter ramets(one-way ANOVA,P<0.05).The highest height,density and aboveground biomass of Carex scabrifolia ramets was significantly reduced due to the competition effects of Scirpus mariqueter seedlings(one-way ANOVA,P<0.05),while density and aboveground biomass of Scirpus mariqueter seedlings was significantly reduced due to the inhibition of Carex scabrifolia ramets(one-way ANOVA,P<0.05).There was intense interspecific competition between ramets and seedlings of sedge plants,which was asymmetric.Competition ability of seedlings was significantly higher than ramets in Scirpus mariqueter seedlings-Carex scabrifolia ramets mixture(one-way ANOVA,P<0.05).(4)Patchiness and heterogeneity of environment factors on small scale had important influence on distribution pattern of salt marsh plant communities,and intraspecific and interspecific interaction would also directly influence the growth and reproduction of plants.Thus,only when we had considered all the factors affecting growth and reproduction of sedge plants,could we thoroughly understand the composition,structure and dynamics of plant communities,which would provide guidance to protection and restoration of native plants in salt marshes.